US20160356180A1

US20160356180A1 - Nacelle inlet having an angle or curved aft bulkhead

Info

Publication number: US20160356180A1
Application number: US14/729,420
Authority: US
Inventors: Eric D. Bol
Original assignee: Boeing Co
Current assignee: Boeing Co
Priority date: 2015-06-03
Filing date: 2015-06-03
Publication date: 2016-12-08
Also published as: CN106240829A; JP6852986B2; CN106240829B; JP2017036033A; EP3103723A1; EP3103723B1

Abstract

A construction of a nacelle inlet aft bulkhead has a curved or angled cross-section configuration between a connection of an outer edge of the aft bulkhead to an outer barrel of the nacelle inlet and a connection of an inner edge of the aft bulkhead to an inner barrel of the nacelle inlet. The curved or angled cross-section configuration of the aft bulkhead gives the bulkhead flexibility to avoid serious damage to the bulkhead in high load cases such as an fan blade off event. The curved or angled cross-section configuration also removes the need for a spring ring attached between the aft bulkhead and the inner barrel of the nacelle inlet. The curved or angled cross-section configuration also provides design flexibility to terminate the outer barrel of the nacelle inlet at an optimized location rearwardly to increase laminar air flow over the nacelle and reduce drag.

Description

FIELD

This disclosure pertains to the construction of a nacelle inlet of an aircraft engine. More specifically, the disclosure is directed to a construction of a nacelle inlet aft bulkhead. The aft bulkhead has a curved or angled cross-section configuration between a connection of an outer edge of the aft bulkhead to an outer barrel of the nacelle inlet and a connection of an inner edge of the aft bulkhead to an aircraft engine fan case attachment ring. The curved or angled cross-section configuration of the aft bulkhead gives the bulkhead flexibility to avoid serious damage to the bulkhead in high load cases such as a fan blade off event. The curved or angled cross-section configuration also removes the need for a spring ring attached between the aft bulkhead and the fan case attachment ring. The curved or angled cross-section configuration also provides design flexibility to terminate the outer barrel of the nacelle inlet at an optimized location rearward of the inner barrel of the nacelle inlet and the aircraft engine fan case attachment ring to extend laminar air flow over the nacelle rearward and reduce drag over the nacelle.

BACKGROUND

FIG. 1 is a representation of the basic component parts that go into the construction of an aircraft engine. The basic component parts include the engine 10 itself that is comprised of a fan 12, an engine fan case 14 surrounding the fan, compressors, combustors, turbines (not shown) inside the engine 10, and an engine exhaust nozzle 16 and exhaust cone 18. The engine 10 is enclosed in a nacelle comprised of a fan cowl 22 and a fan duct/thrust reverser 24. A nacelle inlet 26 is positioned at the forward end of the nacelle.
FIG. 2 represents the nacelle inlet 28 removed from the engine 10 represented in FIG. 1. The nacelle inlet 28 has a general cylindrical configuration with a center axis 30 that defines mutually perpendicular axial and radial directions relative to the nacelle inlet 28. Represented by dashed lines at 32 and 34 are cross-section configurations of the construction of the nacelle inlet at the top of the nacelle inlet and the bottom of the nacelle inlet, respectively. As can be seen in FIG. 2, the cross-section configurations 32, 34 are constructed similarly.
FIG. 3 is a representation of the cross-section configuration 32 of the nacelle inlet 28 at the top of the nacelle inlet as represented in FIG. 2. As represented in FIG. 3, the configuration of the nacelle inlet 28 is defined by a lipskin 38. The lipskin 38 has a nose portion 40 at the forward most end of the nacelle inlet 28, an outer barrel 42 on the exterior of the nacelle inlet 28 and an inner barrel 44 on an interior of the nacelle inlet 28. The nose portion 40 of the lipskin 38 has a general U-shaped cross-section configuration. The outer barrel 42 of the lipskin 38 extends from the nose portion 40 rearwardly to a rear edge 46 of the outer barrel 42. The inner barrel 44 of the lipskin 38 extends rearwardly from the nose portion 40 to a rear edge 48 of the inner barrel. In the representation of FIG. 3, the lipskin 38 extends from the inner barrel 44, around the nose portion 40 of the lipskin 38 and rearwardly across the outer barrel 42 to the rearward edge 48 as one piece. In other constructions, the lipskin 38 could be constructed with the nose portion 40 and outer barrel 42 being separate parts connected by fasteners 50, represent generally in the drawing figures.
An engine fan case attachment ring 52 is connected to the rear edge 48 of the inner barrel 44. The engine fan case attachment ring 52 extends completely around the cylindrical configuration of the nacelle inlet 28. The engine fan case attachment ring 52 is attached to the engine fan case 14. The attachment of the engine fan case attachment ring 52 to the engine fan case 14 supports the nacelle inlet 28 on the engine fan case 14.
There are several bulkheads and stiffeners constructed inside the nacelle inlet 28 that reinforce the construction of the inlet. A forward bulkhead 54 having an annular configuration is secured between the outer barrel 42 and the inner barrel 44 inside the nacelle inlet 28. The forward bulkhead 54 extends completely around a cylindrical configuration of the nacelle inlet 28 and reinforces the nose portion 40 of the lipskin 38.
Several stiffeners 56, 58, 60 are secured to the outer barrel 42 inside the nacelle inlet 28. The stiffeners have L-shaped cross-section configurations and extend completely around the cylindrical configuration of the nacelle inlet 28 reinforcing the outer barrel 42.
An aft bulkhead 62 is secured between the outer barrel 42 and the engine fan case attachment ring 52 inside the nacelle inlet 28. The aft bulkhead 62 has an annular configuration that extends around the cylindrical configuration of the nacelle inlet 28. As represented in FIG. 3, the aft bulkhead 62 has substantially a flat panel structure except for a spring ring 64 having a C-shaped cross-section at an inner edge of the aft bulkhead 62. The spring ring 64 connects an inner edge of the aft bulkhead 62 to the engine fan case attachment ring 52. An outer edge 68 of the aft bulkhead 62 is connected to the outer barrel rear edge 46 by an outer T-ring 70.
The aft bulkhead 62 adds stiffness and rigidity to the construction of the nacelle inlet 28. The aft bulkhead 62 also transmits loads from the engine fan case and the attached engine fan case attachment ring 52 through the aft bulkhead 62 to the outer barrel 42 of the nacelle inlet 28. With the aft bulkhead 62 providing a supporting connection between the outer barrel 42 and the engine fan case attachment ring 52, it is possible that any extreme loads on the engine fan case 12 could be transmitted through the engine fan case attachment ring 52 and through the aft bulkhead 62 to the outer barrel 42 of the nacelle inlet 28 causing excessive damage to the nacelle inlet. Such extreme loads could be produced by a fan blade off event. A fan blade off event is basically the engine fan 12 losing a fan blade that impacts with the fan case 14 at high speed. The fan case 14 is designed to completely contain the fan blade, preventing the fan blade from penetrating the fan case 14. Losing a fan blade at high fan speeds exerts enormous loads on the fan case 14 that are transmitted through the engine fan case attachment ring 52 to the aft bulkhead 62. If the aft bulkhead 62 is too stiff, the transmitted loads from the fan blade off event can deform or shatter the aft bulkhead 62 resulting in the nacelle inlet 28 losing its structural rigidity. To attenuate any such extreme loads, the spring ring 64 is provided at the attachment of the aft bulkhead 62 to the engine fan case attachment ring 52. Thus, the aft bulkhead 62 and the spring ring 64 provide structural rigidity to the nacelle inlet 28, but avoid the transmission of extreme loads from the engine fan case 12 to the outer barrel 42 of the nacelle inlet 28.
However, the construction of the aft bulkhead 62 with the spring ring 64 is disadvantaged in that the design and attachment of the spring ring 64 on the aft bulkhead 62 and the attachment of the spring ring 64 to the engine fan case attachment ring 52 adds complexity, cost and assembly time. Additionally, the flat aft bulkhead 62 that is generally perpendicular to the nacelle inlet center axis 30 requires that the rear edge 46 of the outer barrel 42 be at a specific location relative to the rear edge 48 of the inner barrel 44. This required positioning of the outer barrel rear edge 46 and the inner barrel rear edge 48 may not be optimal to the construction of the nacelle inlet and the performance of the nacelle inlet 28. Additionally, the generally perpendicular configuration of the aft bulkhead 62 necessarily limits the laminar flow of air for a distance over the nacelle inlet 28. The nacelle is designed for a laminar flow of air over the lipskin nose portion 40, over the lipskin outer barrel 42 and to the fan cowl 22. However, the laminar flow gets disrupted and becomes turbulent at the transition from the lipskin outer barrel 42 to the fan cowl 22. Moving this transition rearwardly would reduce drag.

SUMMARY

The nacelle inlet of an aircraft engine of this disclosure includes an angled or curved aft bulkhead that overcomes disadvantages associated with existing aft bulkheads of nacelle inlets while still providing stiffness and rigidity to the nacelle inlet and flexibility to the aft bulkhead.
The nacelle inlet has a lipskin nose at a forward end of the nacelle inlet. An outer barrel extends rearwardly from the lipskin nose on an exterior of the nacelle inlet. The outer barrel extends rearwardly from the lipskin nose to a rear edge of the outer barrel.
An inner barrel extends rearwardly from the lipskin nose on an interior of the nacelle inlet. The inner barrel extends rearwardly from the lipskin nose to a rear edge of the inner barrel.
An engine fan case attachment ring is connected to the rear edge of the inner barrel. The engine fan case attachment ring enables the nacelle inlet to be attached to and supported by the fan case of an aircraft engine.
The angled or curved aft bulkhead is connected between the outer barrel and the inner barrel. The aft bulkhead has an outer edge that is connected to the rear edge of the outer barrel. The aft bulkhead has an inner edge that is connected to the engine fan case attachment ring. The aft bulkhead is configured so that, as the aft bulkhead extends from the inner edge of the aft bulkhead to the outer edge of the aft bulkhead, the aft bulkhead extends rearwardly relative to the nacelle inlet. In one configuration of the aft bulkhead, the aft bulkhead has a rear surface that extends as a flat surface from the inner edge of the aft bulkhead to the outer edge of the aft bulkhead. In a further configuration of the aft bulkhead, the aft bulkhead has a rear surface with a concave configuration between the aft bulkhead inner edge and the aft bulkhead outer edge.
These configurations of the aft bulkhead rear surface enable the rear edge of the outer barrel to be positioned rearwardly of the rear edge of the inner barrel and rearwardly of the engine fan case attachment ring. This provides flexibility in the relative positioning of the rear edge of the outer barrel and the rear edge of the inner barrel of the nacelle inlet and the engine fan case attachment ring. Furthermore, the configurations of the rear surface of the aft bulkhead enables the transition from the lipskin outer barrel to the fan cowl to be moved rearwardly relative to the engine fan case attachment ring. This enables a longer run of laminar air flow over the nacelle and reduces drag.
Still further, the angled or curved configuration of the aft bulkhead enables the aft bulkhead to be connected directly to the lipskin outer barrel eliminating a need for a T-ring connection and provides flexibility in the aft bulkhead and flexibility between the outer barrel and the engine fan case attachment ring connecting the nacelle inlet to the fan case of an aircraft engine. The configurations attenuate forces transmitted to the aft bulkhead from the engine fan case attachment ring and through the aft bulkhead to the outer barrel.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the nacelle inlet of an aircraft engine having an angle or curved aft bulkhead are set forth in the following detailed description and drawing figures.

FIG. 1 is a representation of an exploded view of the basic component parts of an aircraft engine.

FIG. 2 is a representation of a typical nacelle inlet.

FIG. 3 is a representation of a cross-section through the nacelle inlet of FIG. 2 taken at the top of the nacelle inlet.

FIG. 4 is a representation of the nacelle inlet of an aircraft engine of this disclosure having an angled aft bulkhead.

FIG. 5 is a representation of a cross-section of the nacelle inlet of FIG. 4 taken through the top of the nacelle inlet.

FIG. 6 is a representation of the nacelle inlet of an aircraft engine of this disclosure having a curved aft bulkhead.

FIG. 7 is a representation of a cross-section of the nacelle inlet of FIG. 6 taken through the top of the nacelle inlet.

DESCRIPTION

FIGS. 4 and 5 show representations of the nacelle inlet of an aircraft engine of this disclosure that includes an angled aft bulkhead 80 that overcomes disadvantages associated with existing aft bulkheads of nacelle inlets while still providing stiffness and rigidity to the nacelle inlet and flexibility to the aft bulkhead 80. FIGS. 6 and 7 show representations of a nacelle inlet of an aircraft engine that includes a curved aft bulkhead 82 that overcomes disadvantages associated with existing aft bulkheads of nacelle inlets while still providing stiffness and rigidity to the nacelle inlet and flexibility to the aft bulkhead 82. Because both of the aft bulkheads 80, 82 of this disclosure are employed in nacelle inlet constructions such as that of the nacelle inlet 28 described in the background portion of this disclosure, the construction of the nacelle inlet 28 will not again be described in detail herein. It should be understood that the aft bulkheads 80, 82 of this disclosure can be employed in the construction of the nacelle inlet 28 described earlier, or other equivalent nacelle inlets. Because the constructions of the nacelle inlets 28 represented in FIGS. 5 and 7 are basically the same as the nacelle inlet represented in FIG. 3, the same reference numbers employed in FIG. 3 are again employed in the representations of the nacelle inlets 28 of FIGS. 5 and 7 with the reference numbers followed by a prime (′).
Referring to FIGS. 4 and 5, the nacelle inlet 28′ has a lipskin nose 40′ at a forward end of the nacelle inlet 28′. An outer barrel 42′ extends rearwardly from the lipskin nose 40′ and the forward bulkhead 54′ on an exterior of the nacelle inlet 28′. The outer barrel 42′ extends rearwardly from the lipskin nose 40′ to a rear edge 46′ of the outer barrel. Note that the rear edge 46′ of the outer barrel 42′ is moved rearwardly on the nacelle inlet 28 compared to the rear edge 46 of the outer barrel 42 represented in FIG. 3.
An inner barrel 44′ extends rearwardly from the lipskin nose 40 and the forward bulkhead 54′ on an interior of the nacelle inlet 28′. The inner barrel 44′ extends rearwardly from the lipskin nose 40′ and the forward bulkhead 54′ to a rear edge of the inner barrel 48′.
An engine fan case attachment ring 52′ is connected to the inner barrel 44′. The engine fan case attachment ring 52′ is connected to the rear edge 48′ of the inner barrel 44′. The engine fan case attachment ring 52′ enables the nacelle inlet 28′ to be attached to and supported by the fan case of an aircraft engine.
The construction of the nacelle inlet 28′ represented in FIGS. 4 and 5 differs from the construction of the previously described nacelle inlet 28 of FIG. 3 by the aft bulkhead 80 included in the nacelle inlet construction.
The aft bulkhead 80 is secured between the outer barrel 42′ and the engine fan case attachment ring 52′ inside the nacelle inlet 28′. The aft bulkhead 80 has an annular configuration that extends around the cylindrical configuration of the nacelle inlet 28′. The aft bulkhead 80 has a circular outer edge 84 that is connected to the rear edge 46′ of the outer barrel 42′. Note that the connection of the aft bulkhead outer edge 84 is directly to the outer barrel rear edge 46′, eliminating the need and cost for the T-ring 70 represented in FIG. 3. The aft bulkhead 80 also has a circular inner edge 86 that is connected to the engine fan case attachment ring 52. As represented in FIGS. 4 and 5, the aft bulkhead 80 has a substantially flat configuration as it extends between the aft bulkhead outer edge 84 and aft bulkhead inner edge 86. Additionally, the aft bulkhead 80 extends rearwardly relative to the nacelle inlet 28′ as the aft bulkhead extends from its inner edge 86 to its outer edge 84. The angled configuration of the aft bulkhead 80 represented in FIGS. 4 and 5 enables the relative position of the rear edge 46′ of the outer barrel 42′ to be moved relative to the engine fan case attachment ring 52′ simply by changing the angle of the aft bulkhead 80. This flexibility of the relative positions of the rear edge 46′ of the outer barrel 42′ and the engine fan case attachment ring 52′ enables the nacelle inlet 28′ of FIGS. 4 and 5 to be used in a variety of different applications. It also enables the outer barrel rear edge 46′ to be positioned at an optimized location relative to the engine fan case attachment ring 52′. Furthermore, the angled orientation of the aft bulkhead 80 enables the transition from the lipskin outer barrel rear edge 46′ to the fan cowl 22 to be moved rearwardly relative to the engine fan case attachment ring 52′ and relative to the rest of the nacelle. This increases the run of laminar air flow over the nacelle and reduces drag.
Still further, the angled orientation of the aft bulkhead 80 provides flexibility in the aft bulkhead and flexibility between the rear edge 46′ of the outer barrel 42′ and the engine fan case attachment ring 52′. The angled orientation of the aft bulkhead 80 between the engine fan case attachment ring 52′ and the rear edge 48′ of the outer barrel 42′ attenuates forces transmitted through the aft bulkhead 80 from the engine fan case attachment ring 52′ to the rear edge 46′ of the outer barrel 42′.
The construction of the nacelle inlet 28′ represented in FIGS. 6 and 7 differs from the construction of the previously described nacelle inlet 28 of FIG. 3 by the aft bulkhead 82 included in the nacelle inlet construction.
The aft bulkhead 82 is secured between the outer barrel 42′ and the engine fan case attachment ring 52′ inside the nacelle inlet 28. The aft bulkhead 80 has an annular configuration that extends around the cylindrical configuration of the nacelle inlet 28′. The aft bulkhead 82 has a circular outer edge 92 that is connected to the rear edge 46′ of the outer barrel 42′. Again, note that the connection of the aft bulkhead outer edge 92 is directly to the outer barrel rear edge 46′, eliminating the need and cost for the T-ring 70 connection of FIG. 3. The aft bulkhead 82 also has a circular inner edge 94 that is connected to the engine fan case attachment ring 52′. As represented in FIGS. 6 and 7, the aft bulkhead 82 has a curved configuration as it extends between the aft bulkhead outer edge 92 and aft bulkhead inner edge 94. Additionally, the aft bulkhead 82 curves rearwardly relative to the nacelle inlet 28 as the aft bulkhead extends from its inner edge 94 to its outer edge 92. The curved configuration of the aft bulkhead 82 represented in FIGS. 6 and 7 enables the relative position of the rear edge 46′ of the outer barrel 42′ to be moved relative to the engine fan case attachment ring 52′ simply by changing the curvature of the aft bulkhead 82. This flexibility of the relative positions of the rear edge 46′ of the outer barrel 42 and the engine fan case attachment ring 52′ enables the nacelle inlet 28 of FIGS. 6 and 7 to be used in a variety of different applications. It also enables the outer barrel rear edge 46′ to be positioned at an optimized location relative to the engine fan case attachment ring 52′. Furthermore, the curved orientation of the aft bulkhead 82 enables the transition from the lipskin outer barrel rear edge 46′ to the fan cowl 22 to be moved rearwardly relative to the engine fan case attachment ring 52′ and relative to the rest of the nacelle. This increases the run of laminar air flow over the nacelle and reduces drag.
Still further, the curved orientation of the aft bulkhead 82 provides flexibility in the aft bulkhead and flexibility between the rear edge 46′ of the outer barrel 42′ and the engine fan case attachment ring 52′. The curved orientation of the aft bulkhead 82 between the engine fan case attachment ring 52′ and the rear edge 46′ of the outer barrel 42′ attenuates forces transmitted through the aft bulkhead 82 from the engine fan case attachment ring 52′ to the rear edge 46′ of the outer barrel 42′.
As various modifications could be made in the construction of the nacelle inlet and its method of operation herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

Claims

1. A nacelle inlet of an aircraft engine comprising:

a lipskin on a forward end of the nacelle inlet;

an outer barrel on an exterior of the nacelle inlet, the outer barrel extending rearwardly from the lipskin;

an inner barrel on an interior of the nacelle inlet, the inner barrel extending rearwardly from the lipskin; and,

an aft bulkhead on the nacelle inlet, the aft bulkhead having an outer edge connected to the outer barrel and the aft bulkhead having an inner edge connected to the inner barrel, the outer edge of the aft bulkhead being positioned rearwardly of the inner edge of the aft bulkhead.

2. The nacelle inlet of claim 1, further comprising:

an engine fan case attachment ring;

the inner edge of the aft bulkhead being connected to the engine fan case attachment ring;

the inner barrel being connected to the engine fan case attachment ring;

the outer barrel having a rear edge, the outer edge of the aft bulkhead being connected to the rear edge of the outer barrel, and a configuration of the aft bulkhead positioning the rear edge of the outer barrel rearwardly of the engine fan case attachment ring.

3. The nacelle inlet of claim 2, further comprising:

the rearward surface of the aft bulkhead being a smooth, continuous surface that extends between the outer edge of the aft bulkhead and the inner edge of the aft bulkhead.

4. The nacelle inlet of claim 2, further comprising:

the aft bulkhead rearward surface having a concave configuration between the outer edge of the aft bulkhead and the inner edge of the aft bulkhead.

5. The nacelle inlet of claim 2, further comprising:

the rearward surface of the aft bulkhead having a flat configuration between the outer edge of the aft bulkhead and the inner edge of the aft bulkhead.

6. The nacelle inlet of claim 2, further comprising:

the outer edge of the aft bulkhead being positioned rearwardly of the engine fan case attachment ring.

7. The nacelle inlet of claim 2, further comprising:

the outer edge of the aft bulkhead being connected directly to the rear edge of the outer barrel.

8. A nacelle inlet of an aircraft engine comprising:

a lipskin on a forward end of the nacelle inlet;

an outer barrel on an exterior of the nacelle inlet, the outer barrel extending rearwardly from the lipskin to a rear edge of the outer barrel;

an inner barrel on an interior of the nacelle inlet, extending rearwardly from the lipskin to a rear edge of the inner barrel; and,

the rear edge of the outer barrel being positioned rearwardly of the rear edge of the inner barrel.

9. The nacelle inlet of claim 8, further comprising:

an aft bulkhead connected between the rear edge of the outer barrel and the rear edge of the inner barrel.

10. The nacelle inlet of claim 9, further comprising:

the aft bulkhead having an outer edge connected to the rear edge of the outer barrel;

the aft bulkhead having an inner edge connected to the rear edge of the inner barrel; and,

the outer edge of the aft bulkhead being positioned rearwardly of the inner edge of the aft bulkhead.

11. The nacelle inlet of claim 9, further comprising:

an engine fan case attachment ring;

the inner barrel being connected to the engine fan case attachment ring;

12. The nacelle inlet of claim 9, further comprising:

the aft bulkhead having a rearward surface; and,

the aft bulkhead rearward surface being a smooth, continuous surface that extends between the rear edge of the outer barrel and the rear edge of the inner barrel.

13. The nacelle inlet of claim 9, further comprising:

the aft bulkhead having a rearward surface; and,

the rearward surface of the aft bulkhead having a concave configuration between the rear edge of the outer barrel and the rear edge of the inner barrel.

14. The nacelle inlet of claim 9, further comprising:

the aft bulkhead having a rearward surface; and,

the rearward surface of the aft bulkhead having a flat configuration between the rear edge of the outer barrel and the rear edge of the inner barrel.

15. The nacelle inlet of claim 8, further comprising:

an engine fan case attachment ring on the nacelle inlet; and,

the rear edge of the outer barrel being positioned rearwardly of the engine fan case attachment ring.

16. The nacelle inlet of claim 9, further comprising:

an engine fan case attachment ring on the nacelle inlet; and,

the aft bulkhead having an inner edge connected to the engine fan case attachment ring.

17. The nacelle inlet of claim 16, further comprising:

the engine fan case attachment ring being connected to the rear edge of the inner barrel.

18. A method of absorbing force from a fan blade off event exerted on an aft bulkhead of a nacelle inlet where the aft bulkhead does not comprise a spring ring, the method comprising:

connecting an outer edge of the aft bulkhead to an outer barrel of the nacelle inlet and connecting an inner edge of the aft bulkhead to an inner barrel of the nacelle inlet where the aft bulkhead outer edge is positioned rearwardly of the aft bulkhead inner edge.

19. The method of claim 18, further comprising:

configuring a rear surface of the aft bulkhead with a concave configuration between the outer edge of the aft bulkhead and the inner edge of the aft bulkhead.

20. The method of claim 18, further comprising:

configuring a rear surface of the aft bulkhead with a flat configuration that extends between the outer edge of the aft bulkhead and the inner edge of the aft bulkhead.